The present invention relates to an evaporator liquid fuel injection apparatus and fuel cell system, and particularly it relates to an evaporator liquid fuel injection apparatus and fuel cell system whereby appropriate volumes of liquid fuel can be injected based on the requirements for a fuel cell-powered electric vehicle.
Electric vehicles have become well known in recent years as vehicles driven by electrical power sources, and fuel cell-powered electric vehicles are being developed that employ fuel cells as the power source. Some fuel cells used in such fuel cell-powered electric vehicles employ so-called methanol-reformed fuel cells. In such fuel cells, a liquid fuel composed of a mixture of methanol and water, for example, is used and a fuel evaporator is provided which evaporates the liquid fuel and supplies it to a reformer.
The present applicant has disclosed a fuel evaporator for such types of fuel cells in the prior art in Japanese Patent Application No. Hei-1-125366. With reference to FIG. 8, the fuel evaporator 100 is provided with an evaporating chamber 110 wherein liquid fuel FL is evaporated by heated gas HG produced at a combustor (not illustrated) to produce fuel gas FG. The fuel gas FG produced at the evaporating chamber 110 is supplied to a superheating chamber 120 where it is superheated by heated gas HG exiting the evaporating chamber 110. The evaporating chamber 110 and superheating chamber 120 are connected via a guide channel 130 formed along the floor side 110A of the evaporating chamber 110.
In the evaporating chamber 110 there are situated a plurality of U-shaped heat medium tubes 111, 111 . . . through which heated gas HG passes, and the heated gas HG is conveyed toward the guide channel 130. The liquid fuel FL is injected by the liquid fuel injection apparatus 140 toward the heat medium tubes 111, 111 . . . in the evaporating chamber 110. The liquid fuel FL injected by the liquid fuel injection apparatus 140 contacts with the heat medium tubes 111, 111 . . . and undergoes heat exchange to be evaporated. The fuel gas FG produced by evaporation of the liquid fuel FL is supplied to a plurality of vapor tubes 121, 121 . . . situated in the superheating chamber 120.
Meanwhile, the heated gas HG flowing out from the heat medium tubes 111, 111 . . . is supplied to the superheating chamber 120 via the guide channel 130. In the superheating chamber 120, the fuel gas FG passing through the vapor tubes 121, 121 . . . is superheated by the heated gas HG supplied to the superheating chamber 120. The superheated fuel gas FG then flows out from each of the vapor tubes 121, 121 . . . and is supplied to a reformer (not illustrated).
Incidentally, since the pressure in the evaporating chamber varies depending on the effects of adjustment of the anode-cathode pressure difference in the fuel cell, it is difficult to maintain a constant pressure in the evaporating chamber. When liquid fuel is freely injected under conditions where the pressure in the evaporator is not constant, it becomes impossible for the liquid fuel to evenly spread in the evaporating chamber and the efficiency of the liquid fuel evaporation is reduced.
In the aforementioned conventional fuel evaporator 100, however, no particular consideration is made to the relationship between the pressure in the evaporating chamber 110 and the injection volume of the liquid fuel. Consequently, the liquid fuel is simply injected in a volume based on the requirements of a fuel cell-powered electric vehicle.
On the other hand, fuel cell-powered electric vehicles sometimes require rapid huge current for the main motor for times of rapid acceleration and the like. In such situations it is desirable for the huge current to be supplied from the fuel cell as rapidly as possible, but supply of a huge current from the fuel cell requires a large volume of fuel gas. Production of a large volume of fuel gas requires injection of a large volume of liquid fuel and a large amount of heat for evaporation of the large volume of liquid fuel.
In the conventional fuel evaporator 100 described above, however, it is easy to inject a large volume of liquid fuel rapidly but it is not possible to supply a large amount of heat necessary to evaporate the liquid fuel. Consequently, the large volume of liquid fuel cannot be rapidly evaporated, and not only is it impossible to supply the fuel gas rapidly to the fuel cell, but this also results in liquid pools.
It is therefore an object of the present invention to allow efficient evaporation of liquid fuel by injection of a suitable amount of liquid fuel matching the requirements of fuel cells.
It is another object to achieve this even when huge current must be rapidly supplied in situations of rapid acceleration of fuel cell-powered electric vehicles, while also efficiently evaporating supplied liquid fuel and thus preventing liquid pools in the evaporating chamber.
According to a first aspect of the invention, there is provided an evaporator liquid fuel injection apparatus for a fuel evaporator in a fuel cell system, having an evaporating chamber that evaporates liquid fuel with a high temperature heat medium into fuel gas, comprising:
a liquid fuel injection apparatus for injecting said liquid fuel into said evaporating chamber;
an injection volume adjusting apparatus for adjusting the injection volume of the liquid fuel injection apparatus; and
a fuel volume adjusting portion provided in said injection volume adjusting apparatus for setting the liquid fuel injection volume based on an injection volume target setting signal.
With such a construction, an injection volume adjusting portion is provided which sets the fuel injection volume based on an injection volume target setting signal. Consequently, since a suitable volume of liquid fuel can be injected to meet the requirements of the fuel cell, it is possible to efficiently evaporate the liquid fuel.
According to a second aspect of the invention, the aforementioned evaporator liquid fuel injection apparatus is characterized in that said fuel evaporator is provided with a pressure detection means for detecting the pressure in the evaporating chamber, and
said injection volume adjusting portion receives a command value from said pressure detection means and corrects said liquid fuel injection volume.
With such a construction, the pressure in the evaporator is detected by the pressure detection means and the fuel injection volume is corrected according to the command value from the pressure detection means. It is therefore possible to appropriately adjust the injection volume of the liquid fuel according to the pressure conditions in the evaporator. Consequently, the fuel injection volume can be appropriately adjusted even when fluctuations occur in the pressure inside the evaporator.
According to a third aspect of the invention, the aforementioned evaporator liquid fuel injection apparatus is characterized in that said fuel cell system is used in a fuel cell-powered electric vehicle, and
said injection volume target setting signal is an accelerator angle signal.
With such a construction, when the fuel cell system is used in a fuel cell-powered electric vehicle, the injection volume target setting signal is an accelerator angle signal. It is therefore possible to adjust the fuel injection volume according to the accelerator angle, which fluctuates with time in a fuel cell-powered electric vehicle.
According to a fourth aspect of the invention, the aforementioned evaporator liquid fuel injection apparatus is characterized in that said injection volume adjusting portion receives a residue signal from an energy buffer and corrects said liquid fuel injection volume.
With such a construction, the fuel injection volume is corrected by the energy buffer residue signal. In a fuel cell-powered electric vehicle, the required electric power load is supplied not only from the fuel cell but also from an energy buffer such as a battery. Thus, when a large residue is present in the energy buffer, for example, the current supplied from the fuel cell may be reduced. Adjustment is therefore made possible for correction to reduce the fuel injection volume when the current supplied from the fuel cell is to be reduced.
According to a fifth aspect of the invention, the aforementioned evaporator liquid fuel injection apparatus is characterized in that said injection volume adjusting portion corrects said liquid fuel injection volume based on a regeneration signal.
With such a construction, the fuel injection volume is corrected based on a regeneration signal. In a fuel cell-powered electric vehicle, a current is supplied from the main motor to the energy buffer when the main motor is in a regenerating state. Consequently, when it is in a regenerating state, it is possible to reduce the current supplied from the fuel cell. Moreover, since the current supplied from the fuel cell can be reduced during the regenerating state, adjustment is allowed for correction to reduce the fuel injection volume.
According to a sixth aspect of the invention, there is provided a fuel cell system which has a fuel evaporator with an evaporating chamber for evaporation of liquid fuel into fuel gas with a high temperature heat medium, supplies a part of said liquid fuel gas to a fuel cell and supplies the rest together with off gas to said fuel evaporator, the fuel cell system being characterized in that
a fuel utilization volume adjusting means is provided so as to adjust the utilization volume of the liquid fuel gas at the fuel cell, the liquid fuel gas being supplied from said fuel evaporator to the fuel cell according to an injection volume target setting signal,
said fuel evaporator is provided with a liquid fuel injection apparatus for injecting liquid fuel to said evaporating chamber and an injection volume adjusting apparatus for adjusting the injection volume of said liquid fuel injection apparatus, wherein said injection volume adjusting apparatus is provided with an injection volume adjusting portion which supplies a predetermined liquid fuel injection volume based on an injection volume target setting signal, and
when the injection volume target setting signal increases, the utilization volume of the liquid fuel gas at the fuel cell is reduced with said fuel utilization volume adjusting means and thus increasing the liquid fuel gas in said off gas, and an energy buffer compensates for the amount of power lacking due to the decreased utilization volume of said fuel gas while said liquid fuel injection volume is increased with said injection volume adjusting portion.
With such as construction, there is provided a fuel utilization volume adjusting means that adjusts the utilization volume in the fuel cell of the fuel gas supplied to the fuel cell from the fuel evaporator according to an injection volume target setting signal. Consequently, when huge current must be rapidly supplied in a situation of rapid acceleration of a fuel cell-powered electric vehicle, it is possible to temporarily reduce the utilization volume of fuel gas in the fuel cell. Also, an amount of fuel gas equivalent to the reduced fuel utilization volume is supplied to the evaporator together with of f gas in order to increase the amount of heat in the evaporator and achieve rapid evaporation of the large volume of liquid fuel. Since increasing the amount of heat in the evaporator allows rapid evaporation of a large volume of liquid fuel, it is possible to rapidly supply a large volume of fuel gas to the fuel cell.
Here, the current supplied from the fuel cell to the main motor is temporarily insufficient, but the energy buffer can compensate the insufficiency. It can therefore provide satisfactory performance even when it is desired to rapidly supply fuel to the fuel cell in a situation such as rapid acceleration of a fuel cell-powered electric vehicle. Moreover, the supplied liquid fuel can be efficiently evaporated and liquid pools in the evaporating chamber can be prevented.